Cohort studies of children are increasing around the world. A cohort study is a study in which an appropriate number of people of a specific region or group who presently have a certain condition are followed over time to study the factors that affect the condition of each individual and how.

With the increase of children in non-parental child care in the United States since the late 1980s, child care itself has become a much contested issue. Recognizing the importance of this phenomenon, the U.S. federal government appropriated research funds for National Institute of Child Health and Development (NICHD) to initiate a study of major scientific interest and importance called the NICHD Study of Early Child Care. Since the early 1990s, physicians, public health experts, psychologists, educators and other specialists have been following the individual growth and development of newborn infants at ten research sites around the United States.

The findings of the NICHD cohort study have had an enormous impact on those concerned with child care and children's issues. How does attending day care from an early age affect a child's physical growth and emotional/mental development? From specialists to parents, everyone asks this question, but we now know the answer: the NICHD cohort study found no scientific evidence to indicate the early day care caused children any harm.

The First International Symposium on Cohort Studies based on Brain Science was held in Tokyo on November 29, 2005. In her keynote address, Dr. Sarah Friedman of NICHD aroused tremendous interest with her report on the findings of NICHD's cohort study on early child care. Following infants from birth through pre-school and elementary school, the study found that early day care presented no particular problems or detrimental effect. This was predicated, however, on such conditions as the existence of a secure relationship between mother and child, affection by the mother for the child and attachment of the child for the mother, high quality day care and expertise of child care providers, not spending a long time in day care, and infrequent change in the day care provider, etc.

Cohort studies of children are increasingly around the world and this is very important development. In Japan, for example, a cohort study of the effect on media exposure on the development of newborns is now under way. The Ministry of Education, Culture, Sports, Science and Technology is also conducting a cohort study based on brain science to identify social factors that may impact physical development and emotional/mental development of children. The NICHD holds an annual symposium on children's cohort studies. These developments indicate cohort studies will play an increasingly significant role in Child Science as well.